Sardonyx
Chalcedony (quartz)JewelryWiki Editorial·2 sources·Reviewed 2026-08-04
Banded chalcedony alternating reddish-brown sard with white — the material Roman and Renaissance cameo carvers preferred, because the layers let a carver cut a pale figure out of a dark ground in one stone. It is onyx with sard bands rather than black ones.
Properties
| Property | Value | Authority |
|---|---|---|
| Mohs hardness | 7 [1] | — |
| Specific gravity | 2.55–2.91 [1] | — |
| Chemical formula | SiO2 Read from the species entry, Quartz. IGS gives one hardness and density for chalcedony and names its varieties, of which this is one. [2] | — |
| Crystal system | Hexagonal (trigonal), microcrystalline [1] | — |
| Common treatments | Dyeing is standard across banded chalcedony — the same practice that makes most black onyx black. Assume the banding contrast has been enhanced unless told otherwise. [1] | — |
| Care cautions | Keep from acetone and alcohol, which can lift dye, and from prolonged sunlight. [1] | — |
Sources
- International Gem Society — gemstone articles — International Gem Society (IGS, gemstone information articles (gemsociety.org))
- Handbook of Mineralogy — Mineral Data Publishing / Mineralogical Society of America (Handbook of Mineralogy, Mineral Data Publishing)